The disclosure relates generally to additive manufacturing (AM), and more particularly, to a datum structure for use in guiding removal of an object from an AM structure, which may be on an upper surface of an AM build platform.
The pace of change and improvement in the realms of power generation, aviation, and other fields has accompanied extensive research for manufacturing objects used in these fields. Conventional manufacture of metallic, plastic or ceramic composite objects generally includes milling or cutting away regions from a slab of material before treating and modifying the cut material to yield a part, which may have been simulated using computer models, e.g., in drafting software. Manufactured objects which may be formed from metal can include, e.g., airfoil objects for installation in a turbomachine such as an aircraft engine or power generation system.
Additive manufacturing (AM) includes a wide variety of processes of producing an object through the successive layering of material rather than the removal of material. As such, additive manufacturing can create complex geometries without the use of any sort of systems, molds or fixtures, and with little or no waste material. Instead of machining objects from solid billets of material, much of which is cut away and discarded, the only material used in additive manufacturing is what is required to shape the object.
Additive manufacturing techniques typically include taking a three-dimensional computer aided design (CAD) file of the object to be formed, electronically slicing the object into layers, e.g., 18-102 micrometers thick, and creating a file with a two-dimensional image of each layer, including vectors, images or coordinates. The file may then be loaded into a preparation software system that interprets the file such that the object can be built by different types of additive manufacturing systems. In 3D printing, rapid prototyping (RP), and direct digital manufacturing (DDM) forms of additive manufacturing, material layers are selectively dispensed, sintered, formed, deposited, etc., to create the object.
In metal powder additive manufacturing techniques, such as direct metal laser melting (DMLM) (also referred to as selective laser melting (SLM)), metal powder layers are sequentially melted together to form an additive manufacturing (AM) structure that includes the object. More specifically, fine metal powder layers are sequentially melted after being uniformly distributed using an applicator on a metal powder bed. Each applicator includes an applicator element in the form of a lip, brush, blade or roller made of metal, plastic, ceramic, carbon fibers or rubber that spreads the metal powder evenly over the build platform. The metal powder bed can be moved in a vertical axis. The process takes place in a processing chamber having a precisely controlled atmosphere. Once each layer is created, each two dimensional slice of the object geometry can be fused by selectively melting the metal powder. The melting may be performed by a high powered melting beam, such as a 100 Watt ytterbium laser, to fully weld (melt) the metal powder to form a solid metal. The melting beam moves in the X-Y direction using scanning mirrors, and has an intensity sufficient to fully weld (melt) the metal powder to form a solid metal. The metal powder bed may be lowered for each subsequent two dimensional layer, and the process repeats until the AM structure is completely formed. Once the AM structure is complete, at least a portion thereof can be removed from the build platform, creating the final object. In order to create certain larger objects faster, some metal additive manufacturing systems employ more than one high powered laser that work together to form a larger AM structure including the larger object.
Build platforms used in metal powder additive manufacturing typically have a number of desirable attributes. First, an upper surface of the build platform should be installed in horizontal alignment with an applicator of the AM system to ensure even layers of raw material are created. FIG. 1 shows a build platform 10 and its upper surface 12 in a horizontal or non-tilted position, i.e., aligned with an applicator element (not shown). During additive manufacturing, additive manufacturing (AM) structures 14A-C are sequentially built on upper surface 12. Each AM structure 14A-C includes a portion 16A-C therein configured to be an object 18A-C after the object is cut from any remaining portion 20A-C of the AM structure on upper surface 12. More specifically, each AM structure 14A-C includes a removal plane 22A-C extending therein defining an object 18A-C thereabove. Ideally, build platform 10 is horizontal such that removal planes 22A-C are coplanar, and equidistant from upper surface 12 after being formed. That is, build platform 10 is horizontally aligned with the applicator element of the AM system (not shown) so even layers of raw material are created. In this case, a cutting element (not shown)(e.g., that of a wire electrical discharge machine (w-EDM)) would remove each object 18A-E from a remaining portion 20A-C of AM structure 14A-C by cutting parallel to upper surface 12 through removal planes 22A-C, along the dashed line. This process uses zero point clamping devices (not shown) to employ upper surface 12 as a vertical reference plane (not the objects) for guiding the cutting element. Referring to FIG. 2, where build platform 10 is not horizontal in the AM system, the AM system naturally enlarges portions 20A-C during the build of AM structures 14A-C such that objects 18A-C all extend to the same height. Here, when upper surface 12 acts as a vertical reference plane for guiding the cutting element, each object 18A-C is not cut off near the desired final dimensions during the w-EDM process.
A second desirable attribute of a build platform is that it be planar. Build platforms can become non-planar in a number of ways. First, as shown in FIG. 3, during additive manufacturing, build platforms may deform, e.g., due to thermal stress, or the weight of objects 14A-E thereon. Second, build platforms are typically machined between reuses to, for example, remove remaining portions (e.g., 22A-C in FIG. 2) of AM structures. The machining can result in non-planar upper surfaces on the build platform. As shown in FIG. 3, when upper surface 12 acts as a vertical reference plane for guiding the cutting element and it is not planar, each object 14A-E is not cut off near the desired final dimensions during the w-EDM process.
Regardless of whether the build platform is not horizontal or not planar, each resulting object must be extensively machined to remove the unwanted material, which increases cost and time necessary to manufacture each object. The unwanted material oftentimes ends up as waste, diminishing the benefits of the additive manufacturing process.